Hob



'May 19, 1925. 1,538,771

E. WILDHABER HOB FifevdD. 50, 1922 2 Sheets-Sheet l v '1m/Ewan.

A TTORNEY May 19, 1925. 1,538,771

1 E. WILDHABER Ho A Fil'd Dec. so, 1922 sheets-sheet 2 INVENTon ATTORNEY WWA? Wf. 1

Patented May 1Q, 1925.

ERNEST WILDBABER, F BROOKLYN, NEW YORK, ASSIGNOR TO NI'LES-BEMENT-PONDCOMPANY, OF NEW YORK, N. Y.,

A CORPORATION OF NEW JERSEY.

HOB.

Application led December To all whom it may concern.'

Be it known thatl, ERNEST WILDHABER,

a citizen of the Republic of Switzerland,

residing at Brooklyn, in the county of Kings and State of New York,haveinvented certain new and useful Improvements in Hobs, of which thefollowing is a specification.

My invention relates to hobs and particularly to form hobs for shapingmilling cutters. v

One object of my invention is to provide a form hob that shall com riseteeth arranged in the form of la thread), each ofthe teeth having onesubstantially straight cutting l5 edge inclined with respect to the-hobaxis.

Another object of m f invention .is to provide a hob that shall compriseteeth having substantiallystraight cutting edges inclined with respectto the hob ting edge bein Vprovided on one of the end teeth of the hoi.

Another object of my invention is to provide a hob of the aboveindicated character 'that shall have teeth arranged in the form i" of athread on a finishing cutting edge being located on the insider or theoutside of an end tooth of the hob according tothe value of the hobpitch with res ect to the pitchon Athe outside 'of the blan teeth to becut.

Another object ofv my invention is to rfi-. v vide a hob having teetharranged m the v crm of a thread on a conical body portion, the'l teethhaving'cutting edges inclined with respect tothe hob axis and one of theend hob teeth having a finishing cutting edge".

Another object of I vide a hob that shall cut spiral or straight fluteson a blank to form teeth having radial or undercut cutting faces. Afurther ob 'ect of my invention is to provide a conical hob of the aboveindicated character that shall have one iinishin cutting edge on a toothlocated on the sma l end of the hob and that shallrhave a hob pitchdifferent from the outside pitch of the blank to form undercut teeth onthe blank. The formin of radial teeth on a milling cutter by a hobingprocess 'has always been only been feasible to hob milling cutters havinvery short teeth. Even when lhobbing mi ling cutters having very shortlteeth, it l has been diticult to form blank teeth having axis, afinishing cute conical body portion, a-

my invention is to roconsidered a diflic'ult operation and it has- 30,1922.? Serial No. 609,942.

, sharp pointed ends such as are desirable in milling cutters.- Theforming of the blank teeth having spiral flutes increased thediliicultie's .encountered Moreover, the .formingof cutters havingundercut teeth by the hobbing process has hzetofore been deemedpractically impossl e.

Although it is not possible to form under- `cut cutting faces on theteeth of a milling cutter' or other similar article by means of agenerating o eration, it is possible to form such cutting aces by meansof a hobbing operation. The hob used for performing such operation is ofa type sometimes called a form hob. In my vapplications Serial No.609,941 filed December 30, 1922 and Serial N 0. 609,944 filed December30, 1922, the characteristics of form hobs have been discussed. 1 Y y fTh term i form hob in this application is use to designate a. hobwherein the finishing cut is made by one tooth if the hob is singlethreaded. a multiple number of threads, the teeth having finishingcutting edges are increasedin accordance therewith. A, form hob shouldnot shape a blank by a generating o eration, atleast the .finished faceshoul notbe formed by a generating'operation. In ahob constructed inaccordance with myinvention the finishing tooth which' determines theshape of the blank is preferably the last cutting tooth on the hob. l Inthe accompanying drawings: y

Figure 1 -is a diagrammatic view of a hob havinga finishing cuttingvedge aligned with la blank radial llne drawn prpcndicularly to the 'hobaxis.

Fig. 2 is a diagrammatic view illustrating a hob having a pitchdifferent from the blank pitch taken along the outside diameter.

in hobbing cutters.`

If the hob is provided with Y Fig. 3 is a diagrammatic view of a 'conehob having the finishing tooth on the' larger end of the hob;

Fig. 4 is a diagrammatic view of a cone hob having the finishing toothon the smaller end of the hob.

Fig. 5 isa plan view of the hob and blank shown in Fi 2.

Fig. 6 am? Fig. 7 are diagrammatic views of cone hobs having inclinedcutting edges. with respect to the axis of the h ob. l

I respond .to the pitch Fig. 8 is a diagrammatic view of a conc hobaving cutting edges per endicular to the path of movement of the b. eFig. 9 is a plan view of the hob and blank" 6 shown in Fig. 7.

Referring to Fig. l of the drawin a lietil 1 having teeth 2 formed on acy indrical `bogy portion is adapted to rotate on an axis X The hob 1 isshown in engagement with a blank 3 having teeth 4 formed thereon. Theblank 3 is shown rotating'in a clockwise direction on an axis C. The hob1 is shown as rotating in a clockwise direction when viewed from theright offlFig. 1ct the drawings. The hob l. 1s sofset with--re. spect tothe bla k, 3 that atooth 5 on the hob cuts along a radial line CA of theblank, i

. which is disposed perpendicularly to the axisXY ofthehob. mi The hob1, when positioned with respect to the-blank 3, -will nish radial teethon the blank. ...A millin cutter, which is" formed in the above in,icated=manner," ist suitable 'for'cutting slots `in screws and forother similar operaj ions. -It should be noted that the tooth 5 ofthehob 1 extends just to the center line of the blank and accordinglywill cut radial teeth on the blank. Moreover, it should be noted thatthetooth 5 will cutl its own profile or shape on the teeth on the blank.The pitch of a hobshould cor, o the outside diameter of the blank 3. i YThe tooth 5 on the hob performs all finishin cuts whereas the remainingteeth on the ho lperform merely rough work preparatory to the finishingcuts. The hobbing of a blank in the -above indicatedzmanner has. somedrawbacks which vary in accordance wifththesize of the teeth y blank. Ifthe teethitl' comparatively lar then thestrajght cuttingl edgepf thefinis hob will not/cut along a ingtooth 50u-fthe Astraight;@line.ontheblankandthe profile of each"4 to0thoiithe1blankwill be somewhatcurved on account of thehelicoid-al action ofthe hob. It is, of course',apparent that a planing tool would cut along a straight line on theblank if used in place of a hob.- `When a hob operatesv on .a blank,blank rotate in timed relation Ito each other. Accordingly, a hob doesnot Vapply a complete nishing cut on a tooth when the blank 1s in'oneposition. Such curvature onthe blank teeth becomes l.more pronounced ifa multiple thread hob is utilized 'in hobbing theblank.` Moreover, theso.positioning of the radial cutting face of the tooth -5 does not.permit 60 the forming of .spiral flutes on the blank. If such a hob wereused to form spiral lutes, a convex profile of comparatively shacurvature would be formed on the blailili teeth. The operation otthe hobmay be compared with the of spiral flutes flutes,

lis very similar to the operation tooth having to he cut on they`heretofore set -ing position 'the hob and the above mentioned vn'th theplain side of a grinding wheel. It is well, known that it is impossibleto grind spiral fluteswith the lain side of a grinding wheel and thatonli' convex surfaces are produced which spoil the milling cutter beingground. In order to (grind spiral 1t is necessary to provi e a suitableconical grinding wheel. In accordance with the above reasoning, it isapparent that in order to cut spiral flutes, itis desirable to provide ahob having substantially stra-ight cutting edges which are inclined withrespect to the axis of the hob. Thus, it is necessary to provide a hobhaving cutting edges which are angularly disposed with respect to ablank radius which is perpendicular to the hob axis. The operation ofsuch a, form hob of a conical grinding or cutting wheel.

Referring to Figs. 21 and 5 of the drawings, a hob is disclosed havingcutting edges which are inclined with respect to the hob axis. Theinclined cutting edges are obtained by forming a hob with a pitchdifferent 'from the itchat the outside diameter of the blank` A ob 6having teeth 7 formed cn a cylindrical body portion 8- is shown inengagement with a milling cutter blank 9. The hob 6 is rotated in aclockwise .direction on an axis Xf-fY.. and is provided with one aiinishing edge l0 located on the left end of the' hob, as shown in Fig.2 of the drawings. The blank 9 is provided Awith-teeth 11 andisadaptedto rotate on an `from the pitch provi-ded on the hob 1 in Fig.

1 is provided in order to obtain inclined cutting edges.

forth, is made equal to the itch taken at lank. The pitch of the hob 6'is made larger Vthan the pitch taken at the outside diameter of theblank 9.

the outside diameter of the.

The pitch of the hob 1, as

Assuming the tooth 10 to bein the inishi and'the radial line f C-12 tomakean angle a with a radial plane perpendicular to the axis of the hob,the pitch of the rack corresponding to the hub 6 may be obtained in themanner disclosed in my application, Serial No. 609,941. A lineis drawnthrough a point 12 on'the outside'diameter o the blank 9 gerpendicularlyto the radial line C 12.

uch line intersects the line CZ drawn perndicularly to the axis of ythehob at a point 13. 7A line MN drawn through the point 13 parallel to theline of movement of the rack is the pitch line for a rack corresponding'to the hob. Thus, the pitch spending t the circular pitch on the circlehaving a radius equal to C13 is p. In the case of spiral flutes,

of the rack correthe normal pitch I of the rack teeth may beobtaincd bytaking the cosine of the inclination angle of the rack teeth with regardto the blank axis C.

If a rack, ora hob corresponding thereto, is constructed as aboveindicated and is moved to the lett, as shown in Fig. 2 of the' drawings,the teeth to the right of the finishing position, shown in Fig. 2, willnot interfere with the radial profile of the blank tooth. The hob isillustrated in position to finish one blank tooth as heretofore setforth. If the rolling motion between the hob and* the blank werecontinued to the left beyond the illustrated postion, then an involutewould be generated. The generation of an involute would start at theposition illustrated in the drawings and when the tooth 10 was cuttingalong the line C-12.

The position of the tooth 10, as illus- I 2(Vtrated in Fig. 2 of thedrawings, is a limiting position when the hob is provided with a pitchalong the line MN and corresponding to the circular pitch at a radiusC-13. If the pitch should be made larger and the pitch line placedfarther away from the axis of the blank, the positions 'ofthe rack orhob teeth to the right of the illustrated position would not interferewith the radial face of the. blank tooth taken along the line C-12.Moreover, in such case the-illus' limitingA trated position would not bethe position and the position at which the generatino oflan involutewould start. However, the changing ofthe pitch in such manner would formlarger Hutes on the Vblank and accordingly weaken the teeth of theblank.

Thus, as above set forth, by using a form hob corresponding to a rackhaving a pitch differentfrom the pitch of the outside diameter of theblank, 1t is possible to provide a hob having inclined cutting edges.Such cutting edges, as heretofore set forth, operate in a manner similarto a cone grinding Wheel when operating on cutters having helicalfiutes. In my copending application Serial No. 609,943 filed December30, 1922 the specific hob shown in Figs. 2 and 5 is claimed.

Referring to F igs. 3 and 4 of the drawings, another embodiment of myinvention is illustrated. In Fig. 3 a hob 15 having teeth 16 formed on aconical body portion 17 is adapted to rotate on an axis XY. T he hob isillustrated as rotating in a clockwise direction when viewed from theright of Fig. 3 of the drawings. The hob is provided with a finishingtooth 18 which is shown in engagement with the teeth v19 of a blank 20.The blank 20 is'illustrated as ro'- tating in a clockwise direction onan axis C.

A tapered hob of the type disclosed in Fig. 3 and also in Fig. 4 of thedrawings is of particular utility in forming undercut .larger than theings,A it will be noted the roughing teeth are located' to the right ofthe finishing tooth 18 and on the' small end of the cone shaped bodyportion 17. It isdesirable to reverse the position of the teeth in orderto have the finishing tooth on lthe small end ofthe cone body portionand the roughing teeth on the lllarger end thereof. When the roughingteet roughing teeth do more work and save the finishing tooth whichotherwise would assist in roughing the blank.l

pitch of the blank at the outare set ahead of the finishing tooth on thelarge end of the cone body portion, the' Referring to Fig. 4 ofthedrawings, a

hob 21 is illustrated having teeth 22 formed thereon. The hob is adaptedto rotate in a clockwise direction on an axis XY when viewed from theright of Fig.H 4 of the drawlngs. conical body portion end thereof. Inthe 4, the roughing teeth l larger end ofthe cone body portion whereas24 of the hob near the are located on-the A finishing tooth 23 is formedon the.,. n'

hobillustrated in Fig. I

the finishing tooth 23 is located on'A the l smaller end thereof. Thehob 21 is shown in engagement with a blank 25' having teeth 26 formedthereon. The blank 25l is adapted to rotate in a counterclockwisedirection on an axis C". The rack corresponding to the hob 21 shown inFig. fl'of the drawings will be provided with `a pitch p" which issmaller than the pitch p of the outside diameter of the blank 25. Thepitch at the outside diameter of the blank 25 is the same as the pitch7) indicated 3 ofthe drawin -The rack, corresponding ,to the hob 21lsassllmed to have'a'i, path of movement',perpendicular` to fthe radial.line C-.-27 land thef'pitch iii/vas' heretofore set forth, Imust be`equal or smaller-than. the

pitch corresponding Vto a; radius`l QIILLQG, The point-26 is locatedattliebcittom of a radial tooth on the blank...V l f' Generally thelroughing teeth r` are nfiounti ed on the larger end of tbe'tapered h`obif they are located behind the toothl face being finished, as showninFig. 4 ofthe 'drawings or if thel finishing edge is located on theinsideo the last tooth. Such arrangement, which may also be used in caseof cylindrical hobs forming either radial or inclined cutting teeth, hasa further advantage fin ,ting edge is on case the cutter blank is notgroundMatterV of 'such cuttersl isf' When the."rough-v d behindj thecuttingvv located at the smaller end thereof. However, this advantage issomewhat reduced rwlien the blank is lprovided with helical hardening.An example the screw slotting cutter. ing teeth are arrange p' tacebeing finished and [where ',tlie pitch circle @t generation issubstantially le'ss'than the pitch circle t. ken at the outsidediain;

eter oi the blank, the cutting,'edgesiorrnedu on the blank are sharp."otherv fcases where the pitch circle of y eration'is the saine as theoutside diameterIf-'thefzblank. the edges become somewhatlgblunt-In theabove case where the teeth of the hob extend to the side behind thecutting face of the blank which is being finished, it is not necessaryto provide interrupted threads in 'loi-der to obtain sharp edges. f

Attention is called to the fact the racks which correspond tothehobsshov'v/sl in Figs. 3 and 4 of the drawings-are 'provided with toothsides which are perpendicular to the path of movement of the rack.

YHowever, it is possible tonuse tapered hobs having cutting edgesinclined with respect to the said path such as are shown in Fi 2 in thedrawings if so desired In bot cases the cutting edges areA inclined withrespect to the liob axis. .g

` In Figs. 6, 7, 8 and 9, conical hobs lare shown cutting undercut teethon milling cutter blanks. tion of taper or conical hobs may be .said tobe the cutting of undercut :teeth "on milling cutter blanks spiralflutes. In Fig. 6 of the drawings, a hob 30 having teeth 31 formedythereon kis adapted to rotate on an axis XY. The hob is provided with afinishing tooth 32 which is located on the larger end of the hob. Ablank 33 having teeth 34 thereon is adapted to rotate on an axis C2. Theblank 33 is shown rotating in a clockwise direction and the hob 30 isshown rotating in a clockwise direction when viewed from theright ofFig. 6 of the drawings. The cutting faces,

which are formed on the teeth 34 ,of the blank 33, are assumed to beparallel to lines drawn tangent to a circle having a center at C2 andhaving a radius e. The pitch in of the rack or hob corresponds to acircular pitch having a radius C2-35 or (3L-36. It will be noted in Fig.6 the rack or hob teeth assume ppeitions in frontvof the face being 'cuton t the outside of the last tooth of the hob. -Moreover, it should `benoted that a pitch equal to or larger than the pitch p2 insures clearingof lthe teeth. The sides of the teeth of the rack or hob are formedperpendicularly to the path o travel of thev rack.

The conical hob shown in Fig. 6 corresponds somewhat to the hob shown inFig. 3 inasmuch as the finishing. tooth is located on the larger end ofthe hob. As has al- The chief or main applica- P having either straightory e blank. The finishing cut thevhob is more uniformly distributedover uthe teeth if the roughing teeth are located at the larger end andthe finishing tooth is iutes.- Moreover, the advantage is reduced 'inaccordance with the anglel at which the axis.

Figs. 7, 8 and 9 disclose hobs wherein the cutting teeth are arrangedbehind the cutting ktace of the tooth to be cut on the blank and. wherethe finishing cutting edge is locatedoii the inside of tliefhob s lasttooth. The heb shown in Fig. 7 corresponds to a rack with sides whichare perpendicular to .the direction oi' travel of the rack. The pitch ofsuch rack corresponds to the circular pitch at a radius C13-37, thepoint`37 Abeing the intersection point of a line CSZ perpendicular tothe directionof. travel of the rack and a line drawn through the insidelpoint 38 perpendicular to the iute profile of the blank. Fig. 6 and FiA. 7 show the hobs in a position wherein t e generating teeth arehorizontal in order to showanalogy to Fig. 1 and Fig. 2. The hobs mayhob 39 shown in Fig. 7 is provided with teeth 40 which areforined on aconical body portion 41. The finishing tooth 42 is shown in engagementwith the teeth 43 of a blank 44. The hob rotates in a clockwisedirection on an axis XSY3 and the blank rotates in a counterclockwisedirection on an axis C3. The cuttingfaces formed on the teeth of theblank 44 are assumed to be :formed along lines tangent to al cir'clehavin a radius e and a center'at C". The pitc p3 is assumed to be lessthan the pitch taken at the outside diameter of the blank.

InFig. 8 of the drawings, a hob 46 is 'shown provided with teeth 47which are formed on a conical body portion 48. The hob is provided witha finishing tooth '49 which is formed on the smaller end of a hob. Thehob rotates in a clockwise direction on an axis XY and is shown inengagement with a blank 50. YThe blank 50 rotates in a counterclockwisedirection on an axis C4 and is provided with teeth 5l.

The hob 46 shown in Fig. 8 is provided witha larger taper than in Fig.hob 46 moves drawings along the line MN. The tooth sides, it should benoted, are inclined with res ect to the direction of movement of the raccorrespondin `to the hob. rIhe' maximum laced in awhorizcntal position.No d ouble angular setting will be required. in cutting radial orundercut teeth on a blank. The L the hob 39 shown 7. The rackcorresponding to the towards the right as shown i yin Fig. 8 of thepitch to be use on the l one finishing cutting rack may be: found inthesame manner as 1n the cases heretofore considered. It may may be notedthat the steeper hob will prove more satisfactory in service but issomewhat more diiiicult to manufacture. Y

Fig. 9 illustrates a cutting positionxof a conical hob similar to thehob shown in Fig.v 7. The hob is shown to be provided with right handspirals and to cut left :hand spiral fiutes on the blank. The roughinnrteeth cut prior to the finishing tooth atE eac revolution. The roughingteeth are located on the larger end of the conical surface.

It is to be-understood that the abovedescribed action of form hohsrefers merely to the straight cutting edges which cut the flute faces ofthe blanks.1 The other part of the cutting profile may' have agenerating action, if so desired. It should be noted that hobs of theabove indicated type may be made multiple threaded aswell as singlethreaded and may be provided with straight or spiral flutes and withundercut or radial teeth. All of such hobs must be centered and theiraxial position cannot be assumed at will.

. It should be understood that such changes and modifications may bemade in my invention as fall withinthe limits of the appended claims. 'y

What I claim is:

1. A form hob, comprising teeth arranged in the form of a thread andhaving only edge, the teeth having substantially straight cutting edgesinclined with respect to the hob axis and the finishing cutting edgebeing locatedl at one end of the hob.

'2. A form hob having only one finishing cutting edge, comprising teetheach having one substantially straight cutting edge inclined withrespect to the hob axis, the fiub ishing cutting edge being located atthe end of the hob and adapted to be positioned outside a planeperpendicular to the hob axis and radial with respect to the blank beingoperated on.

3. A form hob for cutting iutes, comprising teeth each having onesubstantially straight cutting edge inclined with respect to the hobaxis, the pitch of the hob teeth being different from the pitch of theblank teeth at the outside diameter of theblank.

4. A form hob for cutting helicoidal iiutes` h in a milling cutterblank, comprising teeth each having one straight cutting side inclinedwith respect to the hob axis, a single finishing cutting edge on the hoblocated at the end thereof.

5. A form hob for cutting flutes in a. milling cutter blank,comprisingteeth each havin one substantially straight cutting edgeinclined-with respect to the hob axis, one finishing cutting edge beinglocated at the end of the hob and positioned on one side or the otherside of an end hob tooth according to the'pitch of the hob with respectto the pitch of the teeth being cut.

6. A form hob for cutting flutes in a'milling cutter blank, comprisingteeth each havlng one substantially straight cutting edge cated insidethe last toothiffthe hob pitch is smaller than the pitch of the blankmeasured o'n the outside diameter.

7 A hob, comprising teeth having a pitch different from the pitch of theteeth to be cut on a blank` the cutting edges of the hob teeth whichform the front cutting faces of the blank lteeth being inclined and notperpendicular to the hob axis for cutting teeth having helicoidal frontcutting faces on a'blank. s

8. A hob, comprising teeth having a pitch different from the pitch ofthe teeth to be cut on a blank, the cutting edges of the hob teethwhichform the front cutting faces of the blank teeth being pendicular tothe hob cut teeth on a blank. e

9. A hob comprising teeth arranged in the form of a thread and having apitch when axis for cutting underdifierent from the pitch of the teethto be a cut on a blank.,the cutting edges of the hob teeth which formthe front cutting faces of the blank teeth being inclined andnot-perpendicular to the hob axis, whereby undercut teeth havinghelicoidal front cutting faces may be formed on the blank.

10. A conical hob. comprising teeth arranged in the form of a thread ona conical ody portion. one tooth at the end of the hob being adapted to4effect straight finishing cuts on the teeth of a blank.

11. A conical hob. comprising teeth arranged in the form of a thread ona conical l dy portion, one tooth at the end of the hob having thesmaller diameter being adapted to effect the teeth of a blank.

12. A conical hob, comprising teeth arranged in the form of a thread ona conical bodv portion,

aving the smaller diameter being adapted to effect a straight finishingcuty on the teeth of a blank and the remaining teeth on the hob beingadapted to effect roughing cuts on the teeth of the blank.

13. A conical hob, comprising 'teeth formed on a conical body portion.one of inclined and not perlos straight finishing cuts on said teethserving to effect a finishing cut A on the blank teeth to form undercutteeth.

14. A conical hob, comprising teeth formed on a conical body portion,one tooth at one end of the hob being adapted 'to efon the blank teethto fect finishing cuts to form undercut blank teeth.'

15. A conical hob, comprising teeth formed on a conical body portion,one of said teeth serving to effect a finishing cut form undercut teethhaving helicoidal front cutting faces.A

16. A conical hob, comprising teeth arranged in the form of a thread ona conical body portion, one tooth at the end of the hob having thesmaller diameter being adapted to effect finishing cuts to form`undercutblank teeth.

17. A conical hob, comprising teeth formed on a conical body portion,one tooth at one end of the hob having the smaller diameter serving tocut undercutteeth having helicoidal front cutting faces.

18. A conical hob` comprising teeth formed on a conical body portion,one of said teeth serving to effect a finishing cut on the blank teethto form teeth having helicoidal front cutting faces.

19. A conical hob, comprising teeth arranged in the form of a thread ona conical body portion, the pitch of the hob being smaller than thepitch of the blank to be cut.

20. A conical hob, comprising teeth arranged in the Jform of a thread ona conical body portion, the pitch of the hob being smaller than thepitch of the blank and one tooth at one end of the hob serving to effeetfinishing cuts to form undercut blank teeth.` v

21. A conical portion,

hob having one finishing cutting edge and comprising teeth arranged inthe form of a thread on a conical body portion, each of the teeth havingone substantially straight cutting edge which is inclined with respectto the hob axis and the finishing cutting edge being located at the endof the hob.

22. A conical hob having one finishing cutting edge and comprisingundercut teeth arranged in the form of a thread on a conical bodyportion, each of the teeth having one substantially straightcutting edgewhich is inclined with respect to the hob axis and the finishingcut-ting edge being located at the end of the hob.

23. A conical hob having one finishing cutting edge and comprising teetharranged in the form of a thread on a conical body said teeth havingsubstantially straight cutting edges inclined with respect to the hobedge being located on the inside of an end hob tooth.

24. A conical hob having one finishing cutting edge and comprisingundercut teeth arranged in the form of a thread on a conical bodyportion, the teeth having substantially straight cutting edges inclinedwith respect to the hob axis and the finishing cutting edge beinglocated outside or inside an end tooth on the hob according to the hobpitch with respect to the pitch of the blank being cut.

In testimony whereof, I hereto affix my signature.

ERNEST VVILDHABER.

axis and the finishing cutting Y

